It has long been hypothesized that active sampling in the olfactory system-sniffing-plays a critical role in the processing of odor information. Though sniffing occurs in bouts lasting up to several seconds and containing dozens of individual sniffs, most work addressing the importance of this phenomenon has focused on the first sniff. This proposal expands upon previous work and considers the importance of the entire sniffing bout as it relates to the processing of odors. Three functional hypotheses about the importance of sniffing are examined by analyzing optical signals of olfactory bulb activity in anesthetized and awake mice that are being presented with various odors across a range of sniffing frequencies. Specific attention is paid to how early principal neurons of the olfactory circuit, olfactory sensory neurons and mitral cells, are differentially modulated by sniffing, and how processing by these cells contributes to information coding. Whereas most work on information processing by the olfactory bulb considers mono-molecular odorants, in this project complex mixtures are examined, owing to their importance in the natural environment. By incorporating behaviorally relevant sampling strategies and odor stimuli, the proposed experiments will provide insight into how the initial processing stages of the olfactory system incorporate sniffing-related dynamics to encode odor information.